Gas separation membrane containing metal-organic frameworks and methods of making thereof

ABSTRACT

A membrane including a polymer substrate having pore channels and a metal-organic framework disposed on the polymer substrate. Methods of producing the membrane are described. Methods of separating gases using the membrane are also provided.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a membrane with a metal-organicframework present on a porous polymer substrate. The present inventionalso relates to a method of making the membrane and a method ofseparating a mixture of gases with the membrane.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

The environmental sustainability, cost and energy prospects associatedwith gas separation technology are inevitably accounting for renewedresearch interest in the field. In this regard, membrane gas separationtechnology is a good replacement to conventional technologies likeabsorption and cryogenic distillation which suffer from challenges suchas energy inefficiency. Metal organic frameworks (MOFs) consisting ofmetal and organic linker are highly crystalline porous materials. Thesematerials have received a lot of interest in gas storage [Trickett C A,Helal A. Al-Maythalony B A, Yamani Z H, Cordova K E, Yaghi O M. (2017)Nature Reviews Materials 2:17045, incorporated herein by reference inits entirety], gas separation [Al-Maythalony B A, Alloush A M, Faizan M,Dafallah H, Elgzoly M A A, Seliman A A A, Al-Ahmed A, Yamani Z H, HabibM A M, Cordova K E, Yaghi O M. (2017) ACS Applied Materials & Interfaces9:33401-33407, incorporated herein by reference in its entirety],sensing [Koo W-T, Choi S-J, Jang J-S, Kim I-D. (2017) Scientific Reports7:45074, incorporated herein by reference in its entirety], opticaldevices [Medishetty R, Zareba J K, Mayer D, Samoc M, Fischer R A. (2017)Chemical Society Reviews 46:4976-5004, incorporated herein by referencein its entirety] and catalysis [Dhakshinamoorthy A, Asiri A M, Garcia H.(2017) Chemical Communications 53:10851-10869, incorporated herein byreference in its entirety].

Particularly, MOFs demonstrate potential for separation of gases due totheir controlled pore window, special affinity for different gases andcontrolled composition. However, many reported preparation proceduresyield membranes with defects including cracking and finger voids betweenMOF particles and the support, inhibiting the successful preparation ofa continuous intergrown MOF membrane for gas separation.

Synthesis of nanopore channels were previously attempted [WojciechStarosta B S, Krzysztof Łyczko, Jan Maurin, Andrzej Pawlukojć, LechWaliś, Marek Buczkowski. (2012) NUKLEONIKA 57:581-583; and BozenaSartowskaa W S, Pavel Apelb, O. L Orelovitchb and I. Blonskayab. (2013)CTA PHYSICA POLONICA A 123, each incorporated herein by reference intheir entirety], but such attempts were not successful in growing MOFson nanoporous channels in a membrane.

In view of the forgoing, one objective of the present disclosure is toprovide a membrane with a metal-organic framework disposed on a polymersubstrate having pore channels, a method of preparing the membrane, anda method of utilizing the membrane in gas separation processes.Described herein is the first MOF-containing flexible membrane in whichMOFs are grown in ionic nanopore channels of a polymer substrate. Thisapproach could be used for preparing flexible MOF membranes.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to amembrane comprising a polymer substrate having pore channels and ametal-organic framework comprising a metal ion and an organic ligandcoordinated to the metal ion. The pore channels have an average diameterof 0.1-2 μm and an average length of 2-100 μm, the metal-organicframework is disposed on a wall surface of the pore channels and anouter surface of the polymer substrate, and the metal-organic frameworkis present at an amount of 0.1-50 wt % relative to a total weight of themembrane.

In one embodiment, the metal-organic framework has an average thicknessof 100-2,000 nm.

In one embodiment, the metal ion is an ion of at least one metalselected from the group consisting of a transition metal, apost-transition metal, and an alkaline earth metal.

In one embodiment, the polymer substrate comprises at least onepolyester selected from the group consisting of poly(ethyleneterephthalate), poly(trimethylene terephthalate), poly(butyleneterephthalate), poly(ethylene naphthalate), andpoly(cyclohexylenedimethylene terephthalate).

In one embodiment, the wall surface of the pore channels and the outersurface of the polymer substrate are modified with carboxylate groups.

In one embodiment, the polymer substrate comprises poly(ethyleneterephthalate).

In one embodiment, the organic ligand has at least two carboxylategroups.

In one embodiment, the organic ligand is benzene-1,3,5-tricarboxylate.

In one embodiment, the metal ion is an ion of at least one metalselected from the group consisting of Cu, Zn, Fe, Ni, Co, Mn, Cr, Cd,Mg, Ca, and Zr.

In one embodiment, the metal-organic framework comprises HKUST-1.

In one embodiment, the membrane has an ultraviolet visible absorptionwith an absorption peak of 500-800 nm.

In one embodiment, the membrane has a BET surface area of 100-500 m²/g.

According to a second aspect, the present disclosure relates to a methodof producing the membrane wherein the wall surface of the pore channelsand the outer surface of the polymer substrate are modified withcarboxylate groups. The method involves (i) ion-irradiating a polymersubstrate with heavy ions to form a polymer substrate having latenttracks, (ii) exposing the polymer substrate having latent tracks to alight to form a sensitized polymer substrate, (iii) etching thesensitized polymer substrate with an etchant to form a polymer substratehaving pore channels, (iv) immersing the polymer substrate having porechannels in a first solution comprising the metal ion to form a metalion coated polymer substrate, (v) immersing the metal ion coated polymersubstrate in a second solution comprising the organic ligand to form ametal-organic framework coated polymer substrate, and (vi) alternatingimmersions in the first solution and the second solution for up to 200cycles, thereby forming the membrane. The pore channels have an averagediameter of 0.1-2 μm and an average length of 2-100 μm, and the wallsurface of the pore channels and the outer surface of the polymersubstrate having pore channels are modified with carboxylate groups.

In one embodiment, the heavy ions have a fluence of 10³-10¹⁰ heavy ionsper square centimeter and an average kinetic energy of 5-25 MeV pernucleon.

In one embodiment, the metal ion is present in the first solution at aconcentration of 0.01-100 mM and the organic ligand is present in thesecond solution at a concentration of 0.01-100 mM.

In one embodiment, immersing the polymer substrate having pore channelsin the first solution comprising the metal ion is performed at atemperature of 4-60° C. for 1-60 min per cycle.

In one embodiment, immersing the metal ion coated polymer substrate inthe second solution comprising the organic ligand is performed at atemperature of 4-60° C. for 1-60 min per cycle.

In one embodiment, the etchant is a solution comprising sodium hydroxideat a concentration of 0.5-5 M.

According to a third aspect, the present disclosure relates to a methodof recovering a first gas from a gas mixture comprising the first gasand a second gas. The method involves delivering the gas mixture into afeed side of a chamber containing the membrane of the first aspect thatdivides the chamber into the feed side and a permeate side, such that atleast a portion of the first gas permeates the membrane, and recoveringfrom the permeate side a stream enriched in the first gas compared tothe gas mixture.

In one embodiment, the first gas is hydrogen, carbon dioxide, or both,and the second gas is at least one selected from the group consisting ofoxygen, nitrogen, methane, ethylene, ethane, propylene, and propane.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic representation of the experimental setup of heavyion irradiation and generation of ion tracks [Fleischer R L, Price P B,Walker. R M. 1975. Nuclear tracks in Solids: Principles andApplications. Berkeley: University of California Press; andToimil-Molares M E. (2012) Beilstein J. Nanotechnol. 3:860-883, eachincorporated herein by reference in their entirety].

FIG. 2A is a photo illustrating the sample holder for polymer substratesused during nanopore preparation.

FIG. 2B is a photo illustrating the experimental setup of track etching.

FIG. 2C is a schematic illustration of tracking etching process.

FIG. 3 shows the hydrolysis of ester bonds via chemical etching oftracks in a membrane.

FIG. 4 is a graph illustrating MOF fabrication on a polymer substrateusing liquid phase epitaxy (LPE) approach.

FIG. 5A is a scanning electron micrograph of a cross section of apolyethylene terephthalate (PET) substrate.

FIG. 5B is a scanning electron micrograph of a surface of a PETsubstrate.

FIG. 5C shows a magnified view of the sample in FIG. 5B.

FIG. 6A is a scanning electron micrograph of a surface of a PETsubstrate before HKUST-1 fabrication.

FIG. 6B is a scanning electron micrograph of a surface of a membranefabricated using a 0.5 mmol solution of Cu(II) and a 0.5 mmol solutionof benzene-1,3,5-tricarboxylate.

FIG. 6C is a scanning electron micrograph of a surface of a membranefabricated using a 1 mmol solution of Cu(II) and a 1 mmol solution ofbenzene-1,3,5-tricarboxylate.

FIG. 6D is a scanning electron micrograph of a surface of a membranefabricated using a 2 mmol solution of Cu(II) and a 2 mmol solution ofbenzene-1,3,5-tricarboxylate.

FIG. 6E is a scanning electron micrograph of a surface of a membranefabricated using a 3 mmol solution of Cu(II) and a 3 mmol solution ofbenzene-1,3,5-tricarboxylate.

FIG. 6F is a scanning electron micrograph of a surface of a membranefabricated using a 4 mmol solution of Cu(II) and a 4 mmol solution ofbenzene-1,3,5-tricarboxylate.

FIG. 7A is a scanning electron micrograph of a surface of a PETsubstrate before HKUST-1 fabrication.

FIG. 7B is a scanning electron micrograph of a surface of a membranefabricated by immersion in a solution of Cu(II) for 2 min and in asolution of benzene-1,3,5-tricarboxylate for 4 min after 10 cycles.

FIG. 7C is a scanning electron micrograph of a surface of a membranefabricated by 10 cycles of immersion in a solution of Cu(II) for 5 minand in a solution of benzene-1,3,5-tricarboxylate for 10 min.

FIG. 7D is a scanning electron micrograph of a surface of a membranefabricated by 10 cycles of immersion in a solution of Cu(II) for 10 minand in a solution of benzene-1,3,5-tricarboxylate for 20 min.

FIG. 7E is a scanning electron micrograph of a surface of a membranefabricated by 10 cycles of immersion in a solution of Cu(II) for 15 minand in a solution of benzene-1,3,5-tricarboxylate for 30 min.

FIG. 7F is a scanning electron micrograph of a surface of a membranefabricated by 10 cycles of immersion in a solution of Cu(II) for 30 minand in a solution of benzene-1,3,5-tricarboxylate for 60 min.

FIG. 8A is a scanning electron micrograph of a surface of a membranefabricated via 12 cycles of the LPE process.

FIG. 8B shows a magnified view of the sample in FIG. 8A.

FIG. 8C is a scanning electron micrograph of a cross section of amembrane fabricated via 12 cycles of the LPE process.

FIG. 8D shows a magnified view of the sample in FIG. 8C.

FIG. 9A is a scanning electron micrograph of a surface of a membranefabricated via 2 cycles of the LPE process.

FIG. 9B is a scanning electron micrograph of a surface of a membranefabricated via 20 cycles of the LPE process.

FIG. 9C is a scanning electron micrograph of a surface of a membranefabricated via 40 cycles of the LPE process.

FIG. 9D is a scanning electron micrograph of a surface of a membranefabricated via 60 cycles of the LPE process.

FIG. 9E is a scanning electron micrograph of a surface of a membranefabricated via 80 cycles of the LPE process.

FIG. 9F is a scanning electron micrograph of a surface of a membranefabricated via 100 cycles of the LPE process.

FIG. 10A is a scanning electron micrograph of a cross section of a PETsubstrate before the LPE process.

FIG. 10B is a scanning electron micrograph of a cross section of amembrane fabricated via 20 cycles of the LPE process.

FIG. 10C is a scanning electron micrograph of a cross section of amembrane fabricated via 40 cycles of the LPE process.

FIG. 10D is a scanning electron micrograph of a cross section of amembrane fabricated via 60 cycles of the LPE process.

FIG. 10E is a scanning electron micrograph of a cross section of amembrane fabricated via 80 cycles of the LPE process.

FIG. 10F is a scanning electron micrograph of a cross section of amembrane fabricated via 100 cycles of the LPE process.

FIG. 11A is a scanning electron micrograph of a cross section of amembrane fabricated via 80 cycles of the LPE process.

FIG. 11B is an energy dispersive X-ray spectroscopy (EDX) spectrum ofthe sample in FIG. 11A.

FIG. 12A is an overlay of powder X-ray diffraction (PXRD) patterns of aPET substrate, membranes fabricated via various (20, 40, 60, 80, 100)cycles of the LPE process and a simulated PXRD pattern of HKUST-1.

FIG. 12B is an expanded view of the overlay in FIG. 12A between 3 to 20degrees 2-theta.

FIG. 13A is an overlay of ultraviolet-visible (UV-vis) absorbancespectra of a PET substrate and membranes fabricated via various (20, 40,60, 80, 100) cycles of the LPE process.

FIG. 13B is an expanded view of the overlay in FIG. 13A from 550 nm to800 nm.

FIG. 14A is a photo showing the transparency nature of a membranefabricated via 100 cycles of the LPE process.

FIG. 14B is a first photo showing the flexibility of the sample in FIG.14A.

FIG. 14C is a second photo showing the flexibility of the sample in FIG.14A.

FIG. 15A is a scanning electron micrograph of a membrane after beingsoaked in toluene for 1 hour and then sonicated for 5 seconds.

FIG. 15B shows a magnified view of the sample in FIG. 15A.

FIG. 15C is a scanning electron micrograph of a membrane after beingsoaked in toluene for 1 hour and then sonicated for 10 seconds.

FIG. 15D shows a magnified view of the sample in FIG. 15C.

FIG. 15E is a scanning electron micrograph of a membrane after beingsoaked in toluene for 1 hour and then sonicated for 60 seconds.

FIG. 15F shows a magnified view of the sample in FIG. 15E.

FIG. 15G is scanning electron micrograph of a membrane after beingsoaked in toluene for 1 hour and then sonicated for 300 seconds.

FIG. 15H shows a magnified view of the sample in FIG. 15G.

FIG. 16A is an overlay of thermogravimetric curves of a PET substrateand a membrane fabricated via 100 cycles of the LPE process.

FIG. 16B is an expanded view of the overlay in FIG. 16A between 0-300°C.

FIG. 16C is an expanded view of the overlay in FIG. 16A between 550-740°C.

FIG. 17A is a photo of a membrane before activation.

FIG. 17B is a photo of the membrane in FIG. 17A after activation at 100°C.

FIG. 18 is an atomic force microscopy (AFM) analysis of a membranefabricated via 100 cycles of the LPE process.

FIG. 19 is a graph illustrating N₂ adsorption/desorption isotherms of amembrane fabricated via 100 cycles of the LPE process at 77 K.

FIG. 20 is an overlay of CO₂ adsorption/desorption isotherms of amembrane at 273 K, 298 K, and 308 K.

FIG. 21 is an overlay of CO₂, CH₄, and N₂ adsorption/desorptionisotherms of a membrane at 298 K.

FIG. 22 is a graph illustrating the calculation of isosteric heat ofadsorption (Q_(st)).

FIG. 23 is a schematic illustration of aconstant-volume/variable-pressure (CV/VP) gas permeation setup.

FIG. 24 is an overlay of single gases (H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₂H₄,C₃H₈, C₃H₆) permeation against time for a membrane at 308 K and 1.0 bar.

FIG. 25 is a bar graph illustrating ideal separation factors of H₂against different gases (O₂, N₂, CO₂, CH₄, C₂H₆, C₂H₄, C₃H₈, C₃H₆) for amembrane at 308 K and 1.0 bar.

FIG. 26 is a bar graph illustrating ideal separation factors of CO₂against different gases (N₂, CH₄, C₂H₆, C₂H₄, C₃H₈, C₃H₆) for a membraneat 308 K and 1.0 bar.

FIG. 27 is a graph illustrating the relationship between the diffusioncoefficients of single gases (H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₂H₄, C₃H₈,C₃H₆) for a membrane at 308 K and the Lennard-Jones diameter of therespective gases.

FIG. 28 is a graph illustrating the relationship between the sorptioncoefficients (S) of single gases (H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₂H₄,C₃H₈, C₃H₆) for a membrane at 308 K and the normal boiling points of therespective gases.

FIG. 29 is a graph illustrating CO₂/CH₄ relationship by plotting gaspair selectivity (a) against CO₂ permeability (P) in comparison with theRobeson upper bound curve [Robeson L M. (2008) Journal of MembraneScience 320:390-400, incorporated herein by reference in its entirety].

FIG. 30 is a graph illustrating CO₂/N₂ relationship by plotting gas pairselectivity (a) against CO₂ permeability (P) in comparison with theRobeson upper bound curve [Robeson L M. (2008) Journal of MembraneScience 320:390-400, incorporated herein by reference in its entirety].

FIG. 31 is a graph illustrating H₂/CH₄ relationship by plotting gas pairselectivity (a) against H₂ permeability (P) in comparison with theRobeson upper bound curve [Robeson L M. (2008) Journal of MembraneScience 320:390-400, incorporated herein by reference in its entirety].

FIG. 32 is a graph illustrating H₂/N₂ relationship by plotting gas pairselectivity (a) against H₂ permeability (P) in comparison with theRobeson upper bound curve [Robeson L M. (2008) Journal of MembraneScience 320:390-400, incorporated herein by reference in its entirety].

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown.

As used herein, the words “a” and “an” and the like carry the meaning of“one or more”. Within the description of this disclosure, where anumerical limit or range is stated, the endpoints are included unlessstated otherwise. Also, all values and subranges within a numericallimit or range are specifically included as if explicitly written out.

It must be noted that, as used in the specification and the appendedclaims, the overall surface area of the polymer substrate primarilyconsists of the wall surface of the pore channels and the outer surfaceof the polymer substrate.

For polygonal shapes, the term “diameter”, as used herein, and unlessotherwise specified, refers to the greatest possible distance measuredfrom a vertex of a polygon through the center of the face to the vertexon the opposite side. For a circle, an oval, an ellipse, and amultilobe, “diameter” refers to the greatest possible distance measuredfrom one point on the shape through the center of the shape to a pointdirectly across from it.

According to a first aspect, the present disclosure relates to amembrane comprising a polymer substrate having pore channels and ametal-organic framework comprising a metal ion and an organic ligandcoordinated to the metal ion. The metal-organic framework may be presentat an amount of 0.1-50 wt %, 0.5-40 wt %, 1-30 wt %, 5-20 wt %, or 10-15wt % relative to a total weight of the membrane.

In one or more embodiments, the pore channels are present in the polymersubstrate at a density of 10²-10⁷/mm², 10³-10⁶/mm², or 10⁴-10⁵/mm².Depending on the size of the polymer substrate, it may have at least 10²pore channels, at least 10³ pore channels, at least 10⁴ pore channels,at least 10⁵ pore channels, at least 10⁶ pore channels, at least 10⁷pore channels, or at least 10⁷ pore channels. In one or moreembodiments, the polymer substrate has at least 50%, at least 75%, atleast 90%, or at least 95% of the total number of pore channelsextending through the entire thickness of the polymer substrate. In atleast one embodiment, a plurality of pore channels present does notextend through the entire thickness of the polymer substrate. In one ormore embodiments, the pore channels have an average length of 2-500 μm,preferably 4-400 μm, preferably 6-300 μm, preferably 8-200 μm,preferably 10-100 μm, preferably 12-50 μm, preferably 15-25 μm.

In one or more embodiments, the pore channels are randomly arranged inthe polymer substrate, i.e. distances between a pore channel and itsneighboring pore channels are different. Alternatively, the porechannels are evenly arranged in the polymer substrate, i.e. a distancebetween a pore channel and all its neighbors is the same orsubstantially the same. The distance can be said to be substantially thesame when the shortest distance is at least 80%, at least 85%, at least90%, or at least 95% of the average distance and the longest distance isnot more than 120%, not more than 110%, or not more than 105% of theaverage distance. The distance is measured from a center of a porechannel to a center of a neighboring pore channel and may be in a rangeof 1 nm to 1 m, 10-800 nm, 50-600 nm, 100-400 nm, or 200-300 nm.Energy-dispersive X-ray spectroscopy, X-ray microanalysis, elementalmapping, transmission electron microscopy, scanning electron microscopy,and scanning transmission electron microscopy may be useful techniquesfor observing the arrangement of the pore channels in the polymersubstrate.

The cross-section of the pore channels may be of any desired shape, suchas a circle, an oval, an ellipse, a multilobe, and a polygon. In one ormore embodiments, the openings of the pore channels have an averagediameter of 0.01-3 μm, preferably 0.05-2.5 μm, preferably 0.1-2.0 μm,preferably 0.15-1.0 μm, preferably 0.2-0.8 μm, preferably 0.25-0.6 μm,preferably 0.3-0.4 μm. The wall surface (i.e. internal surface) of thepore channels may contain ridges, dimples, knurls, flutes, or otherperturbations. The cross-section of the pore channels may be constantover the length of pore channels or may vary over the length. In apreferred embodiment, the pore channels are uniform throughout theentire thickness of the polymer substrate and are of a cylindricalshape. In another embodiment, the pore channels are conical-shaped orelongated oval-shaped (cigar-shaped).

The pore channels may be straight or substantially straight. In someembodiments, the pore channels may extend through the polymer substratewithout intersecting one another. In some embodiments, pore channelspresent in the polymer substrate are separated from each otherthroughout their respective length. In at least one embodiment, the porechannels are parallel or substantially parallel to each other (e.g.forming a monolith-like structure). In another embodiment, pore channelsin the polymer substrate are randomly oriented and may intersect (e.g.,forming a sponge-like pore structure).

In one or more embodiments, the polymer substrate comprises a polyester.Suitable polyesters include those commonly prepared by condensationpolymerization of hydroxyl-containing monomers and/or oligomers withpoly-acid-containing monomers and/or oligomers. Exemplaryhydroxyl-containing monomers useful in the preparation of the polyestersinclude aliphatic diols, e.g. ethylene glycol, 1,2-propylene glycol,1,3-propylene glycol, 2,2-dimethyl-1,3-propane diol,2-ethyl-2-methyl-1,3-propane diol, 1,4-butane diol, 1,4-but-2-ene diol,1,3-1,5-pentane diol, 1,5-pentane diol, dipropylene glycol, and2-methyl-1,5-pentane diol, cycloaliphatic diols, e.g. 1,6-hexane diol,dimethanol decalin, dimethanol bicyclooctane, 1,4-cyclohexanedimethanol, triethylene glycol, and 1,10-decanediol. Examples ofpoly-acid-containing monomers that can be used to prepare the polyestersinclude isophthalic acid, terephthalic acid,1,2-di(p-carboxyphenyl)ethane, 4,4′-dicarboxydiphenyl ether,4,4′-bisbenzoic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalenedicarboxylic acid, decahydronaphthalene dicarboxylic acids, norbornenedicarboxylic acids, bicyclooctane dicarboxylic acids,1,4-cyclohexanedicarboxylic acid, 1,4-hexylenedicarboxylic acid, adipicacid, azelaic acid, dicarboxyl dodecanoic acid, and succinic acid. Thepoly-ester counterparts of the aforementioned poly-acid-containingmonomers and/or oligomers such as dimethyl terephthalate, dimethyl2,6-naphthalenedicarboxylate may also be used in preparing the polyesterthrough transesterification reactions.

Specific examples of polyesters include, but are not limited to,poly(ethylene terephthalate), poly(1,4-butylene terephthalate),poly(ethylene naphthalate), poly(trimethylene terephthalate),poly(butylene naphthalate), poly(1,3-propylene terephthalate),poly(1,4-cyclohexylenedimethylene terephthalate),poly(1,4-cyclohexylenedimethylene 1,4-cyclohexanedicarboxylate),poly(1,4-cyclohexylenedimethylene terephthalate-co-isophthalate),poly(cyclohexylenedimethylene-co-ethylene terephthalate),poly(butylene-co-poly(oxytetramethylene) terephthalate),poly(butylene-co-poly(oxyethylene) terephthalate),poly(1,4-cyclohexylene dimethylene co-ethylene terephthalate), andpoly(ethylene-co-1,4-cyclohexylenedimethylene terephthalate). In apreferred embodiment, the polymer substrate comprises at least onepolyester selected from the group consisting of poly(ethyleneterephthalate), poly(trimethylene terephthalate), poly(butyleneterephthalate), poly(ethylene naphthalate), andpoly(cyclohexylenedimethylene terephthalate). In a more preferredembodiment, the polymer substrate comprises poly(ethyleneterephthalate).

Polyesters that can be used herein as the polymer substrate furtherinclude polyacrylates such as poly(methyl methacrylate), poly(ethylmethacrylate), and other polymers which are cured forms of a resincomposition comprising a methacrylate monomer including, withoutlimitation, methyl methacrylate (MMA), 2-hydroxyethyl methacrylate(HEMA), isopropyl methacrylate, n-propyl methacrylate, isopropylmethacrylate, n-butyl methacrylate, isobutyl methacrylate, hydroxyethylmethacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate,propylene glycol monomethacrylate, isobornyl methacrylate,methoxyethoxyethyl methacrylate, ethoxyethoxyethyl methacrylate,tetrahydrofurfuryl methacrylate, acetoxyethyl methacrylate,phenoxyethylmethacrylate, methacryloyloxyethyl phthalate (MEP),bisphenol A-glycidyl methacrylate (bis-GMA), urethane dimethacrylate(UDMA), triethylene glycol dimethacrylate (TEGDMA), ethoxylatedbisphenol A dimethacrylate (bis-EMA), ethyleneglycol dimethacrylate,diethyleneglycol dimethacrylate, trimethyleneglycol dimethacrylate,glycerol dimethacrylate, trimethyolpropane trimethacrylate,tetraethyleneglycol dimethacrylate, 1,3-propanediol dimethacrylate,1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate,1,12-dodecanediol dimethacrylate, polyethyleneglycol dimethacrylate,bismethacryloyloxymethyltricyclo-[5.2.1.]decane (TCDMA),trimethylolpropane trimethacrylate, 1,2,4-butanetriol trimethacrylate,pentaerythritol tetramethacrylate, diurethane dimethacrylate (DUDMA),and pyromellitic acid glycerol dimethacrylate (PMGDM), and mixturesthereof.

Conventional hydroxyl or carboxylate functionalized solid substrates arebrittle and provide non-uniform growth of anchor agents thereby causingdefects while handling and tightening during testing. Ionic channels inthe cell membrane may facilitate the selective transportation of ionicspecies across the membrane. Considering the functional features andeffectiveness of ionic channels, artificial ionic nanopore channels maybe prepared in a polymer substrate using the swift heavy ion irradiationand chemical etching process. The chemical formation of MOF in the ionicnanopores may open the way to a new strategy for various applications ofmetal-organic materials.

The heavy ion irradiation and subsequent chemical etching process of thepolymer substrate (e.g. polyethylene terephthalate (PET)) generatesnative carboxyl groups (—COOH) and hydroxyl groups (—OH) on the wall ofnanopore polymer. These carboxyl groups are utilized for anchoring MOFssuch as HKUST-1 [Cu₃(benzene-1,3,5-tricarboxylate)₂, or Cu₃(btc)₂].HKUST-1 is known as potential candidate for gas storage, separation,catalytic performance and other characteristics including ionic andelectrical conductivity properties [Soleimani Dorcheh A, Denysenko D,Volkmer D, Donner W, Hirscher M. (2012) Microporous and MesoporousMaterials 162:64-68, incorporated herein by reference in its entirety].

In a preferred embodiment, the wall surface (i.e. internal surface) ofthe pore channels and the outer surface of the polymer substrate aremodified with carboxylate groups. The density of the number ofcarboxylate groups on the surfaces of the polymer substrate may rangefrom 0.01-100/nm², preferably 0.1-10/nm², preferably 0.2-5/nm²,preferably 0.4-4/nm², preferably 0.6-3/nm², preferably 0.8-2/nm², orabout 1/nm². In another embodiment, the wall surface of the porechannels and the outer surface of the polymer substrate are modifiedwith hydroxyl groups. Carboxyl and/or hydroxyl functionalities on asurface of the polymer substrate (e.g. polyester) may serve to increasethe hydrophilicity of the substrate and thus enhance attachment ofhydrophilic inorganic species and metal-organic frameworks to thesubstrate.

The metal-organic framework comprises a metal ion which is an ion of atleast one metal selected from the group consisting of a transition metal(e.g. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd,Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, andCn), a post-transition metal (e.g. Al, In, Ga, Sn, Bi, Pb, Tl, Zn, Cd,and Hg), and an alkaline earth metal (e.g. Be, Mg, Ca, Sr, Ba, and Ra).Further, these metal ions may be of any oxidation state M⁺¹, M⁺², M⁺³,etc. In one or more embodiments, the metal ion is an ion of at least onemetal selected from the group consisting of Cu, Zn, Fe, Ni, Co, Mn, Cr,Cd, Mg, Ca, and Zr. In a preferred embodiment, the at least one metal isCu. The metal ion is preferably Cu(II).

Chemical species containing 1,3,5-benzenetricarboxylate linkerscoordinated to small tetrahedral metals have been grown on aluminasupports functionalized with —COOH, —OH and Au [Guerrero V V, Yoo Y,McCarthy M C, Jeong H-K. (2010) Journal of Materials Chemistry20:3938-3943, Nan J, Dong X, Wang W, Jin W, Xu N. (2011) Langmuir27:4309-4312, and Hurrle S, Friebe S, Wohlgemuth J, WOII C, Caro J,Heinke L. (2017) Chemistry—A European Journal 23:2294-2298, eachincorporated herein by reference in their entirety], copper net [Guo H,Zhu G, Hewitt I J, Qiu S. (2009) Journal of the American ChemicalSociety 131:1646-1647, incorporated herein by reference in itsentirety], hollow ceramic fibers (HCFs) [Zhou S, Zou X, Sun F, Zhang F,Fan S, Zhao H, Schiestel T, Zhu G. (2012) Journal of Materials Chemistry22:10322-10328, incorporated herein by reference in its entirety],anodic aluminum oxide (AAO) [Mao Y, Cao W, Li J, Sun L, Peng X. (2013)Chemistry—A European Journal 19:11883-11886, incorporated herein byreference in its entirety], copper hydroxide nanostrand (CHN) [Mao Y,shi L, Huang H, Cao W, Li J, Sun L, Jin X, Peng X. (2013) ChemicalCommunications 49:5666-5668, incorporated herein by reference in itsentirety], polyvinylidene difluoride (PVDF) [Mao Y, Li J, Cao W, Ying Y,Sun L, Peng X. (2014) ACS Applied Materials & Interfaces 6:4473-4479,incorporated herein by reference in its entirety], stainless steel [ZhuH, Liu H, Zhitomirsky I, Zhu S. (2015) Materials Letters 142:19-22,incorporated herein by reference in its entirety], copper oxide [Guo Y,Mao Y, Hu P, Ying Y, Peng X. (2016) ChemistrySelect 1:108-113,incorporated herein by reference in its entirety], ionic liquid/chitosan(IL-CS) [Fernandez-Barquín A, Casado-Coterillo C, Etxeberria-BenavidesM, Zuñiga J, Irabien A. (2017) Chemical Engineering & Technology40:997-1007, incorporated herein by reference in its entirety]. However,none of the above mentioned support could provide a flexible membrane.

In the formation of a metal organic framework, the organic ligands mustmeet certain requirements to form coordination bonds, primarily beingmultidentate, having at least two donor atoms (i.e. O—, and/or N—) andbeing neutral and/or anionic. The structure of the metal organicframework is also affected by the shape, length, and functional groupspresent in the organic linker. In certain embodiments, the metal organicframework of the present disclosure comprises anionic ligands as organicligands. In one or more embodiments, the organic ligands may have atleast two carboxylate groups. Preferably, the organic ligands arepolycarboxylates including, but not limited to, di-, tri-, tetra-,and/or hexacarboxylates. In a most preferred embodiment, the metalorganic framework of the present disclosure in any of its embodimentscomprises benzene-1,3,5-tricarboxylate as the organic ligands.Benzene-1,3,5-tricarboxylate organic ligands have carboxylate groups,with each carboxylate groups forming a coordinative bond to the metalions (e.g. Cu(II)) to produce a coordination network. Preferably, themetal-organic framework comprises HKUST-1.

It is equally envisaged that the metal organic framework of the presentdisclosure may be adapted to further comprise one or more additionalorganic ligands in addition to or in lieu of thebenzene-1,3,5-tricarboxylate ligands including, but not limited to,bidentate carboxylates, tridentate carboxylates, tetradentatecarboxylates, azoles, and neutral ligands. Exemplary suitable bidentatecarboxylates include, but are not limited to carboxylates forms ofoxalic acid (ethanedioic acid, HOOC—COOH), malonic acid (propanedioicacid, HOOC—(CH₂)—COOH), succinic acid (butanedioic acid,HOOC—(CH₂)₂—COOH), glutaric acid (pentanedioic acid, HOOC—(CH₂)₃—COOH),phthalic acid (benzene-1,2-dicarboxylic acid, o-phthalic acid,C₆H₄(COOH)₂), isophthalic acid (benzene-1,3-dicarboxylic acid,m-phthalic acid, C₆H₄(COOH)₂), terephthalic acid(benzene-1,4-dicarboxylic acid, BDC, p-phthalic acid, C₆H₄(COOH)₂),biphenyl-4,4′-dicarboxylic acid, BPDC, HOOC—(C₆H₄)₂—COOH), and the like.Exemplary tridentate carboxylates include, but are not limited to,carboxylates forms of 1,2,3-benzenetricarboxylic acid,1,2,4-benzenetricarboxylic acid, citric acid(2-hydroxy-1,2,3-propanetricarboxylic acid,(HOOC)CH₂C(OH(COOH)CH₂(COOH), 1,3,5-tris(4-carboxyphenyl)benzene, andthe like. Exemplary tetradentate carboxylates include, but are notlimited to, carboxylates forms of 1,2,4,5-benzenetetracarboxylic acid,biphenyl-3,3′,5,5′-tetracarboxylic acid,1,2,3,4-cyclobutanetetracarboxylic acid, 1,2,3,4-butanetetracarboxylicacid, and the like. Exemplary azoles include, but are not limited to,1,2,3-triazole (1H-1,2,3-triazole, C₂H₃N₃), pyrrodiazole(1H-1,2,4-triazole, C₂H₃N₃), and the like. Exemplary suitable neutralligands included, but are not limited to, piperazine and4,4′-bipyridine.

A particle is defined as a small object that behaves as a whole unitwith respect to its transport and properties. The metal-organicframework of the present disclosure in any of its embodiments may be inthe form of particles of the same shape or different shapes, and of thesame size or different sizes. An average diameter (e.g., averageparticle diameter) of the particle, as used herein, refers to theaverage linear distance measured from one point on the particle throughthe center of the particle to a point directly across from it. Themetal-organic framework particles may have an average diameter in arange of 10-200 nm, 50-150 nm, or 75-100 nm. The metal-organic frameworkparticles may be agglomerated or non-agglomerated (i.e., themetal-organic framework particles are well separated from one anotherand do not form clusters). In one embodiment, the metal-organicframework particles are agglomerated and the agglomerates have anaverage diameter in a range of 1-20 μm, 2-15 μm, or 5-10 μm.

The metal-organic framework particles may be spherical or substantiallyspherical (e.g., oval or oblong shape). In some embodiments, themetal-organic framework particles are in the form of at least one shapesuch as a sphere, a rod, a cylinder, a rectangle, a triangle, apentagon, a hexagon, a prism, a disk, a platelet, a flake, a cube, acuboid, and an urchin (e.g., a globular particle possessing a spikyuneven surface). The metal-organic framework may be mesoporous ormicroporous. An average pore size of the metal-organic frameworkparticle may be in a range of 0.1-10 nm, 0.2-5 nm, 0.4-3 nm, or 0.8-2nm.

In one or more embodiments, the aforementioned metal-organic frameworkis disposed on the wall surface of the pore channels and the outersurface of the polymer substrate. The metal-organic framework mayinteract with the carboxylate groups on the wall surface of the porechannels and/or the outer surface of the polymer substrate throughcoordinate bonding. The metal-organic framework particles may alsointeract with the surfaces of the polymer substrate via van der Waalsforces and/or π-π interactions (for polymer substrates containing arylgroups such as phenyl, naphthyl, anthracenyl and bipbenyl). Themetal-organic framework preferably covers greater than 90%, greater than95%, greater than 96%, greater than 97%, greater than 98%, greater than99%, greater than 99.5% of the wall surface of the pore channels of thepolymer substrate. The metal-organic framework preferably covers greaterthan 90%, greater than 95%, greater than 96%, greater than 97%, greaterthan 98%, greater than 99%, greater than 99.5% of the outer surface ofthe polymer substrate. In one or more embodiments, the metal-organicframework has an average thickness of 50-4,000 am, preferably 100-3,000nm, preferably 200-2,500 nm, preferably 300-2,000 nm, preferably400-1,800 nm, preferably 600-1,600 nm, preferably 800-1,400 nm,preferably 1,000-1,200 nm.

As used herein, UV-vis spectroscopy or UV-vis spectrophotometry refersto absorption spectroscopy or reflectance spectroscopy in theultraviolet-visible spectral region. In one or more embodiments, themembrane has an ultraviolet visible absorption with an absorption peakin a range of 450-900 nm, preferably 500-800 nm, preferably 600-750 nm,preferably 680-720 nm, or about 700 nm. It should be noted that theabsorption peak intensity of the membrane increases as the thickness ofthe metal-organic framework increases.

The Brunauer-Emmet-Teller (BET) theory (S. Brunauer, P. H. Emmett, E.Teller, J. Am. Chem. Soc. 1938, 60, 309-319, incorporated herein byreference) aims to explain the physical adsorption of gas molecules on asolid surface and serves as the basis for an important analysistechnique for the measurement of a specific surface area of a material.Surface area is a property of solids which is the total surface area ofa material per unit of mass, solid or bulk volume, or cross sectionalarea. In most embodiments, BET surface area is measured by gasadsorption analysis, preferably N₂ adsorption analysis. In a preferredembodiment, the membrane has a BET surface area of 50-500 m²/g,preferably 75-400 m²/& preferably 100-300 m²/g, preferably 125-280 m²/g,preferably 150-260 m²/g, preferably 170-240 m²/g, preferably 190-220m²/g, preferably 200-210 m²/g.

The membrane disclosed herein may be a thin film membrane, a flat sheetmembrane, or a spiral membrane. The membrane may be in the form ofvarious shapes, for example, flat (e.g., for a disc-shaped membrane),bent, curved (e.g., a cylinder shaped membrane), and rippled. As shownin FIGS. 14A, B and C, the membrane is relatively transparent andflexible. It can be flipped, bent, and/or curved without causing defectsin the membrane structure. In one embodiment, the membrane is a thinfilm membrane and has a thickness of 10-500 μm, 50-400 μm, or 100-300μm. In some embodiments where the membrane is disc-shaped, a diameter ofthe membrane may be 10-100 mm, 11-80 mm, or 12-50 mm. In someembodiments, the membrane is in a form of a rectangular sheet having awidth of 2-110 cm, 10-70 cm, or 20-60 cm. A length of the rectangularsheet may range from 10 cm to 122 m, 100 cm to 50 m, 1 m to 20 m, or 5in to 10 m.

The membranes may be freestanding or supported on or by a substrate. Thesubstrate may be macroporous and may establish the lateral dimensionsand shape of the membranes as they are being formed. Further, thesubstrate provides the finished membrane with structural stability.Examples of materials from which the substrate can be made are ceramics,glass, metals, and polymers. Exemplary ceramics include, withoutlimitation, α-Al₂O₃, γ-Al₂O₃, η-Al₂O₃, θ-Al₂O₃, χ-Al₂O₃, κ-Al₂O₃,δ-Al₂O₃, silica, titania, magnesia, zirconia, and combinations thereof.Exemplary metals include, without limitation, gallium, germanium,stainless steel, titanium, and combinations thereof. Exemplary polymersinclude, without limitation, polysulfones, polyether sulfones,polyacrylonitriles, cellulose esters, polypropylenes, polyvinylchlorides, polyvinylidene fluorides, polyarylether ketones, polyamides(e.g., nylons), and polyesters. A wide variety of suitable substratesare either available commercially or may be prepared using techniquesknown to those of ordinary skill in the art. The substrate may bepresent in an amount of at least 10%, at least 20%, at least 30%, atleast 40%, at least 50%, or at least 75% by weight based on a combinedweight of the membrane and the substrate.

While the substrate may serve a filtering function by size exclusion,its filtering characteristics (if any) may be substantially more coarsethan those of the membrane itself. In terms of pore size, the supportcan have pores with an average diameter in a range of 100 nm to 50 μm,500 nm to 20 μm, or 1-10 μm in diameter. The pore sizes should besufficiently large so that a permeate gas can pass through the supportwithout reducing the permeability of the membrane. However, the poresshould not be so large that the membrane will either be unable to bridgeor form across the pores, or tend to fill up or penetrate too far intothe pores, thus producing an effectively thicker membrane than thethickness described herein.

According to a second aspect, the present disclosure relates to a methodof producing the membrane wherein the wall surface of the pore channelsand the surface of the polymer substrate are modified with carboxylategroups. The method involves (i) ion-irradiating an initial polymersubstrate with heavy ions to form a polymer substrate having latenttracks, (ii) exposing the polymer substrate having latent tracks to alight to form a sensitized polymer substrate, (iii) etching thesensitized polymer substrate with an etchant to form a polymer substratehaving pore channels, (iv) immersing the polymer substrate having porechannels in a first solution comprising the metal ion to form a metalion coated polymer substrate, (v) immersing the metal ion coated polymersubstrate in a second solution comprising the organic ligand to form ametal-organic framework coated polymer substrate, and (vi) alternatingimmersions in the first solution and the second solution for up to 200cycles, preferably 10-180 cycles, preferably 20-160 cycles, preferably40-140 cycles, preferably 60-120 cycles, preferably 80-100 cycles,thereby forming the membrane.

Ion-irradiation may be performed using swift heavy-ion beams generatedby large accelerator facilities, e.g. the universal linear accelerator(UNILAC) of GSI (Darmstadt, Germany), and the cyclotrons at GANIL (Caen,France), JINR (Dubna, Russia), CICLONE (Louvain la Neuve, Belgium),Lanzhou (China), and Brookhaven (USA). Exemplary heavy-ions useful inthe currently disclosed ion-irradiation include, but are not limited to,²³⁸U, ¹⁹⁷Au, ²⁰⁶Pb, and ²⁰⁹Bi. In one or more embodiments, the heavyions have an average kinetic energy of 5-25 MeV per nucleon, preferably6-20 MeV, preferably 7-15 MeV, preferably 8-14 MeV, preferably 9-13 MeV,preferably 10-12 MeV, or about 11.4 MeV per nucleon.

Ion-irradiation of the initial polymer substrate with swift heavy-ionbeams may result in the generation of damaged zones which are definedherein as latent tracks (see FIG. 1). These latent tracks are producedmainly due to the breakdown of chemical bonds, leading to the productionof double and triple bonds via ionization and electric excitationsduring high energy ions interacting with the initial polymer substrate[Sun Y, Zhu Z, Wang Z, Jin Y, Liu J, Hou M, Zhang Q. (2003) Nucl. Instr.& Method. B 209:188-193, incorporated herein by reference in itsentirety]. The applied heavy-ion fluence may be altered in order to varythe density of latent tracks in the substrate. Higher latent trackdensities may lead to overlaps in polymer substrate later produced.Moreover, outgassing of volatile fragments leads to a decrease inmaterial density along the ion tracks. The amount of damage induced inthe latent track may depend on the energy loss of the heavy ions alongtheir passage through the initial substrate. In one or more embodiments,the heavy ions have a fluence of 10³-10¹⁰ heavy ions per squarecentimeter, preferably a fluence of 10⁴-10⁹, 10⁵-10⁸, or 10⁶-10⁷ heavyions per square centimeter.

Track cores in polymer membranes having latent tracks are mainlycomposed of chemically active polymer fragments, which can undergopost-irradiation reactions, such as oxidation, photo-oxidation, etc. Asa result, storage of the ion-irradiated polymer membranes in air leadsto a significant increase in the rate of etching. Energy deposited byultraviolet (UV) light may further increase the rate of etching andselectivity by breaking chemical bonds along the latent track. UV lightillumination may increase the surface polarity and thus facilitate theetchant attack on the polymer substrate having latent tracks. Inaddition to etching rate enhancement, UV light illumination may lead toimprovement in pore size distribution [Zhu Z, Maekawa Y, Liu Q, YoshidaM. (2005) Nucl. Instrum. Methods Phys. Res., Sect. B:61-67, incorporatedherein by reference in its entirety]. Illumination with light atwavelengths longer than 320 nm increases the track etching rate (V_(T),latent tracks area). Illumination with light at wavelengths shorter than320 nm enhances both track etching rate (V_(T)) and bulk etching rate(V_(B), undamaged area) of the polymer substrate. Latent tracks in apolymer membrane can also be effectively sensitized by the treatmentwith certain organic solvents [Dobrev D, Trautmann C, Neumann R. (2006)GSI Scientific Report:321, incorporated herein by reference in itsentirety].

In a preferred embodiment, the polymer substrate having latent tracks isexposed to a light before etching. The light may be UV light having awavelength of 200-400 nm, preferably 250-350 nm, more preferably 270-330nm. The light source may comprise one or more wavelengths within therange of 200-400 nm. In certain embodiments, the light may be providedby a light source offering the photon energy necessary to sensitize thepolymer substrate having latent tracks of the present disclosure in anyof their embodiments. Exemplary light sources include, but not limitedto, a black light lamp, a short-wave UV lamp, an incandescent lamp, agas-discharge lamp, a UV LED, and a UV laser. The polymer substratehaving latent tracks may be exposed to the light for 0.1-4 hours, 0.5-2hours, or about 1 hour.

Light sensitized polymer membranes may be exposed to a suitable etchantsolution. During the etching process, the damaged zone (latent iontracks) in polymer membrane is removed and converted into a hollow pore.The geometry of the pore channels depends on the ratio of track etchingrate (V_(T), latent tracks area) to bulk etching rate (V_(B), undamagedarea). Latent ion tracks are converted into pore channels when the tracketching rate is higher than the bulk etching rate [Apel P Y, Blonskaya IV, Oganessian V R, Orelovitch O L, Trautmann C. (2001) Nucl. Instrum.Methods Phys. Res., Sect. B 185:216-221, incorporated herein byreference in its entirety].

For the case of PET (also known as polyester) membrane, the polymer isformed through a network of ester bonds via the condensation betweenterephthalic acid and ethylene glycol. The etchant (e.g. NaOH) primarilyattacks these ester bonds. The alkali hydrolyses these partially chargedester bonds in the polymer chain, leading to the production of carboxyl(—COOH) and hydroxyl (—OH) groups on the surface (see FIG. 3) [PasternakC A, Alder G M, Apel P Y, Bashford C L, Edmonds D T, Korchev Y E, Lev AA, Lowe G, Milovanovich M, Pitt C W, Rostovtseva T K, Zhitariuk N I.(1995) Radiat. Meas. 25:675-683; Maekawa Y, Suzuki Y, Maeyama K,Yonezawa N, Yoshida M. (2004) Chemistry Letters 33:150-151; Maekawa Y,Suzuki Y, Maeyama K, Yonezawa N, Yoshida M. (2006) Langmuir22:2832-2837; Chen W, McCarthy T J. (1998) Macromolecules 31:3648-3655,each incorporated herein by reference in their entirety]. It wasestimated that the density of carboxyl groups on the inner pore wallswas ˜1 group nm⁻². [Wolf-Reber A. (2002). Aufbau einesRasterionenleitwertmikroskops. Stromfluktuationen in Nanoporen in: PhDDissertation, Vol. PhD, Johann Wolfgang Goethe Universität, Frankfurt amMain, Germany. Frankfurt am Main, pp. 3-89825-89490-89829,dissertation.de, incorporated herein by reference in its entirety]

In one or more embodiments, the polymer substrate having latent tracksis subjected to an etchant. Preferably, sodium hydroxide is used as theetchant. Exemplary additional alkalines that may be used in addition to,or in lieu of sodium hydroxide include, but are not limited to,potassium hydroxide, calcium hydroxide, magnesium hydroxide, lithiumhydroxide, or mixtures thereof. When used in solution, the alkaline maybe dissolved in water prior to etching the polymer substrate havinglatent tracks. In one embodiment, the etchant is a solution comprisingsodium hydroxide at a concentration of 0.5-5 M, preferably 1-4 M,preferably 2-3M. Alternatively, an acidic etchant is used. Exemplaryacidic etchants include, without limitation, hydrochloric acid, sulfuricacid, nitric acid, phosphoric acid, boric acid, hydrofluoric acid,hydrobromic acid, hydroiodic acid, perchloric acid, and the like.

A symmetric etching is performed by immersing the polymer substratehaving latent tracks in an etchant where the concentration of theetchant and the temperature in the vicinity of the polymer substrate arekept approximately constant throughout the entire etching process.Conversely, an unsymmetrical etching may be carried out by exposing thepolymer substrate having latent tracks to an environment where theconcentration of the etchant and/or the temperature is different in thevicinity of the polymer substrate. In a preferred embodiment, asymmetric etching is performed on the polymer substrate having latenttracks through constant stirring of the etchant for a pre-set timeaccording to a required pore diameter (e.g. the pore diameter growslinearly with etching time at a rate of about 4-5 nm per minute) at20-80° C., preferably 30-70° C., preferably 40-60° C., or about 50° C. Apolymer substrate having pore channels (e.g. a perforated substrate) maybe collected after etching, soaked and/or washed with water. In one ormore, the perforated polymer substrate has pore channels with an averagediameter of 0.01-3 μm, preferably 0.05-2.5 μm, preferably 0.1-2.0 μm,preferably 0.15-1.0 μm, preferably 0.2-0.8 μm, preferably 0.25-0.6 μm,preferably 0.3-0.4 μm, and an average length of 2-500 μm, preferably4-400 μm, preferably 6-300 μm, preferably 8-200 μm, preferably 10-100μm, preferably 12-50 μm, preferably 15-25 μm, and the wall surface ofthe pore channels and the surface of the perforated polymer substrateare modified with carboxylate groups. Alternatively, a perforatedpolymer substrate having pore channels with varied cross-sections overthe length of the pore channels (e.g. conical-shaped and elongatedoval-shaped pore channels) may be prepared by unsymmetrical etching.

In one or more embodiments, the aforementioned metal ion is present inthe first solution at a concentration of 0.01-100 mM, preferably 0.1-50mM, preferably 0.5-10 M, preferably 1-5 M. In one or more embodiments,the aforementioned organic ligand is present in the second solution at aconcentration of 0.01-100 mM, preferably 0.1-50 mM, preferably 0.5-10 M,preferably 1-5 M. Solvents used for the first and the second solutionsmay be chosen for their ability to completely dissolve the metal ion andthe organic ligand and for ease of solvent removal in the membraneformation step. Exemplary solvents include alcohols, e.g. methanol,ethanol, trifluoroethanol, n-propanol, i-propanol, n-butanol, i-butanol,t-butanol, n-pentanol, i-pentanol, 2-methyl-2-butanol,2-trifluoromethyl-2-propanol, 2,3-dimethyl-2-butanol, 3-pentanol,3-methyl-3-pentanol, 2-methyl-3-pentanol, 2-methyl-2-pentanol,2,3-dimethyl-3-pentanol, 3-ethyl-3-pentanol, 2-methyl-2-hexanol,3-hexanol, cyclopropylmethanol, cyclopropanol, cyclobutanol,cyclopentanol, and cyclohexanol, ethers such as diethyl ether,tetrahydrofuran, 1,4-dioxane, tetrahydropyran, t-butyl methyl ether,cyclopentyl methyl ether, and di-iso-propyl ether, ketones such asacetone, esters such as ethyl acetate and propyl acetate, hydrocarbonssuch as pentane and hexane, and chlorinated solvents such asdichloromethane and chloroform. Preferably, ethanol is chosen as thesolvent.

Highly ordered MOF coatings can be prepared via liquid-phase epitaxy(LPE). This method has the advantages over other methods as it providesa well-defined thickness, orientation and absence of defects. Epitaxyrefers to the deposition of a crystalline overlayer on a substrate.Liquid-phase epitaxy (LPE) is an epitaxial technique that uses solutionsto grow crystals on a substrate. In one embodiment, the currentlydisclosed membranes are fabricated in a multi-step LPE process byalternating deposition of the metal ion and the organic ligand on theaforementioned polymer substrate having pore channels.

Alternating immersions in the first solution and the second solution mayinvolve one or more of (i) immersing the polymer substrate having porechannels in the first solution comprising the metal ion for 1-60minutes, 2-30 minutes, or 5-10 minutes at a temperature of 4-60° C.,10-40° C., 15-30° C., or about 22° C. to absorb a portion of the metalion onto at least a surface of the polymer substrate (e.g. the wallsurface of the pore channels and an outer surface of the polymersubstrate), (ii) withdrawing the polymer substrate from the firstsolution, (iii) draining excess liquid from the polymer substrate (e.g.evaporating the solvent by drying in air for 1-10 minutes, 2-8 minutes,or 3-5 minutes), (iv) washing the polymer substrate with a solvent (e.g.ethanol) to form a metal ion coated substrate, (v) immersing the metalion coated substrate in the second solution comprising the organicligand for 1-60 minutes, 2-30 minutes, or 5-10 minutes at a temperatureof 4-60° C., 10-40° C., 15-30° C., or about 22° C. to absorb a portionof the organic ligand onto at least a surface of the substrate (e.g. thewall surface of the pore channels and an outer surface of the polymersubstrate), (vi) withdrawing the substrate from the second solution,(vii) draining excess liquid from the polymer substrate (e.g.evaporating the solvent by drying in air for 1-10 minutes, 2-8 minutes,or 3-5 minutes), (viii) washing the polymer substrate with a solvent(e.g. ethanol), (iv) repeating aforementioned steps on the samesubstrate for up to 200 cycles, preferably 10-180 cycles, preferably20-160 cycles, preferably 40-140 cycles, preferably 60-120 cycles,preferably 80-100 cycles, thereby forming the membrane. Alternatively,the membrane may be prepared by a LPE process by placing the polymersubstrate having pore channels in a growth solution comprising both themetal ion and the organic ligands.

According to a third aspect, the present disclosure relates to a methodof recovering a first gas from a gas mixture comprising the first gasand a second gas. The method involves delivering the gas mixture into afeed side of a chamber containing the membrane of the first aspect thatdivides the chamber into the feed side and a permeate side, such that atleast a portion of the first gas permeates the membrane, and recoveringfrom the permeate side a stream enriched in the first gas compared tothe gas mixture. The stream enriched in the first gas may be subjectedto further processing steps such as an additional purification step(e.g. column chromatography, further membrane separation steps, etc.).

In one or more embodiments, a force is provided to deliver the gasmixture into the feed side. For example, the gas mixture introduced intothe feed side of the chamber has a pressure of 1-5 bar, preferably 1.1-4bar, preferably 1.2-3 bar, preferably 1.3-2 bar, preferably 1.4-1.8 bar,preferably 1.5-1.7 bar. In one embodiment, the method also involvesapplying a reduced pressure (i.e. vacuum) to the permeate side of thechamber. In one or more embodiments, the gas mixture is introduced at atemperature of 20-60° C., 25-50° C., 30-40° C., or about 35° C.

Gases that may be separated by the membrane disclosed herein in any ofits embodiments include, without limitation, hydrogen, carbon dioxide,carbon monoxide, oxygen, nitrogen, hydrocarbons having 1-4 carbon atoms(e.g. methane, ethane, ethylene, acetylene, propane, propylene, butane,iso-butane), and noble gases (e.g. helium, neon, argon, krypton, xenon).In a preferred embodiment, the first gas is hydrogen, carbon dioxide, orboth, and the second gas is at least one selected from the groupconsisting of oxygen, nitrogen, methane, ethylene, ethane, propylene,and propane.

The membrane disclosed herein may have a permeability of at least 500barrer, at least 1000 barrer, at least 2,000 barrer, at least 3,000barrer, at least 3,500 barrer and up to 6,000 barrer, up to 5,000barrer, up to 4,500 barrer, or up to 4,000 barrer, for hydrogen gas. Themembrane may have a permeability of at least 100 barrer, at least 200barrer, at least 400 barrer, at least 600 barrer, or at least 800barrer, and up to 2,000 barrer, up to 1,500 barrer, or up to 1,000barrer, for oxygen gas. The membrane may have a permeability of at least100 barrer, at least 150 barrer, at least 200 barrer, at least 250barrer, and up to 500 barrer, up to 400 barrer, or up to 300 barrer, fornitrogen gas. The membrane may have a permeability of at least 2,000barrer, at least 3,000 barrer, at least 4,000 barrer, or at least 4,500barrer, and up to 7,000 barrer, up to 6,000 barrer, or up to 5,000barrer, for carbon dioxide gas. The membrane may have a permeability ofat least 50 barrer, at least 100 barrer, at least 250 barrer, or atleast 500 barrer, and up to 800 barrer, up to 700 barrer, or up to 600barrer, for methane, ethane, ethylene, propane, and/or propylene. Thepermeability measurements may be taken at an upstream pressure of 1.1-5bar, 1.5-4 bar, or 1.8-2.5 bar, and the membrane may be pre-evacuated at20-50° C., 35-45° C., or 30-40° C.

Barter is a non-SI unit of gas permeability used in the membranetechnology.

${1\mspace{14mu} {barrer}} = {10^{- 10}\frac{{cm}_{STP}^{3} \cdot {cm}}{{cm}^{2} \cdot s \cdot {cmHg}}}$

Here, the term “cm³ _(STP)” is standard cubic centimeter, which is aunit of amount of gas rather than a unit of volume. It represents theamount of gas molecules or moles that would occupy one cubic centimeterat standard temperature and pressure, as calculated via the ideal gaslaw. The term “cm” corresponds, in the permeability equations, to thethickness of the material whose permeability is being evaluated, theterm “cm³ _(STP) cm⁻²s⁻¹” corresponds to the flux of gas through thematerial, and the term “cmHg” corresponds to the pressure drop acrossthe material. Thus, “barrer” is a measure of the rate of fluid flowthrough an area of material with a thickness driven by a given pressure.In SI units, 1 barrer is equivalent to 3.34×10⁻¹⁶ mol Pa⁻¹ s⁻¹ m⁻¹.

As used herein, the term “ideal selectivity” refers to a ratio betweenthe permeability of the gases. The ideal selectivity of H₂/N₂ of themembrane disclosed herein may be at least 4, at least 8, or at least 10,and up to 20, up to 15, or up to 12. The ideal selectivity of H₂/O₂ ofthe membrane may be at least 5, at least 8, or at least 12, and up to30, up to 20, or up to 15. The ideal selectivity of H₂/CO₂ of themembrane may be at least 2, at least 4, or at least 6, and up to 12, upto 10, or up to 8. The ideal selectivity of H₂/CH₄ of the membrane maybe at least 5, at least 8, or at least 12, and up to 30, up to 20, or upto 15. The ideal selectivity of H₂/C₂H₆ of the membrane may be at least4, at least 6, or at least 8, and up to 20, up to 16, or up to 12. Theideal selectivity of H₂/C₂H₄ of the membrane may be at least 5, at least10, or at least 15, and up to 40, up to 30, or up to 20. The idealselectivity of H₂/C₃H₈ of the membrane may be at least 40, at least 60,or at least 80, and up to 120, up to 100, or up to 90. The idealselectivity of H₂/C₃H₆ of the membrane may be at least 80, at least 100,or at least 120, and up to 200, up to 175, or up to 150. The idealselectivity of CO₂/N₂ of the membrane may be at least 4, at least 8, orat least 15, and up to 30, up to 25, or up to 20. The ideal selectivityof CO₂/CH₄ of the membrane may be at least 4, at least 8, or at least15, and up to 30, up to 25, or up to 20. The ideal selectivity ofCO₂/C₂H₆ of the membrane may be at least 3, at least 6, or at least 9,and up to 20, up to 15, or up to 12. The ideal selectivity of CO₂/C₂H₄of the membrane may be at least 5, at least 10, or at least 15, and upto 35, up to 25, or up to 20. The ideal selectivity of CO₂/C₃H₈ of themembrane may be at least 50, at least 70, or at least 90, and up to 140,up to 120, or up to 100. The ideal selectivity of CO₂/C₃H₆ of themembrane may be at least 90, at least 120, or at least 140, and up to200, up to 180, or up to 160.

Any given pair or group of gases that differ in molecular sizes, forexample, hydrogen and nitrogen, hydrogen and oxygen, hydrogen and carbondioxide, hydrogen and methane, hydrogen and ethane, hydrogen andethylene, hydrogen and propane, hydrogen and propylene, carbon dioxideand nitrogen, carbon dioxide and methane, carbon dioxide and ethane,carbon dioxide and ethylene, carbon dioxide and propane, carbon dioxideand propylene, nitrogen and oxygen, helium and methane, can be separatedusing the membrane described herein. More than one gas may be removedfrom the gas mixture. For example, a stream enriched in the first gascompared to the gas mixture may be recovered from the permeate side byremoving the second gas including oxygen, nitrogen, methane, ethylene,ethane, propylene, and/or propane.

In some embodiments, the method is useful in enriching hydrogen gas froma gas mixture comprising hydrogen gas and nitrogen gas, or hydrogen gasfrom a gas mixture comprising hydrogen gas and carbon dioxide gas, orhydrogen gas from a gas mixture comprising hydrogen gas and methane gas,or hydrogen gas from a gas mixture comprising hydrogen gas and ethanegas, or hydrogen gas from a gas mixture comprising hydrogen gas andethylene gas, or hydrogen gas from a gas mixture comprising hydrogen gasand propane gas, or hydrogen gas from a gas mixture comprising hydrogengas and propylene gas. In other embodiments, the method is useful inenriching carbon dioxide gas from a gas mixture comprising carbondioxide gas and nitrogen gas, or carbon dioxide gas from a gas mixturecomprising carbon dioxide gas and methane gas, or carbon dioxide gasfrom a gas mixture comprising carbon dioxide gas and ethane gas, orcarbon dioxide gas from a gas mixture comprising carbon dioxide gas andethylene gas, or carbon dioxide gas from a gas mixture comprising carbondioxide gas and propane gas, or carbon dioxide gas from a gas mixturecomprising carbon dioxide gas and propylene gas.

The chamber used for separating the gas mixture may be of any shape solong as the membrane can be securely housed and utilized inside thechamber to accomplish the gas mixture separation. For example, thechamber may be a cylindrical membrane module. The chamber may alsoinclude an inlet configured to accept feed material, a first outletconfigured to expel a retentate, and a second outlet configured to expela permeate. The chamber can be configured to be pressurized so as topush feed material though the inlet, retentate through the first outletand permeate through the second outlet. The chamber may also include avacuum pump to provide vacuum or a reduced pressure to the permeateside. Further, it is contemplated that at least 2, 3, 4 or more of thesame or different membranes disclosed herein may be used in series withone another to further enrich or isolate a targeted gas from a gasmixture. Similarly, the membranes may be used in series with othercurrently known membranes to enrich or isolate a targeted gas from a gasmixture.

In addition to gas separation and enrichment, the membranes disclosedherein may be used in separation of liquid mixtures by pervaporation,water treatment, air purifiers, chemical filters, oil and gasrefineries, fermenters, and bioreactors.

The examples below are intended to further illustrate protocols forpreparing, characterizing and utilizing the membrane, and are notintended to limit the scope of the claims.

Example 1 Fabrication of Cylindrical Nanopores Polymer Irradiation

The irradiation of polymer membranes was performed with swift heavy ions(²³⁸U, ¹⁹⁷Au or ²⁰⁶Pb) having a kinetic energy of up to 11.4 MeV pernucleon. The irradiation of polyethylene terephthalate sheet wasperformed at a heavy ion accelerator UNILAC (Universal LinearAccelerator) at GSI Helmholtzzentrum für Schwerionenforschung GmbH,Darmstadt, Germany. This linear accelerator is 120 m long and has theability to accelerate the heavy ions up to ˜15% of the speed of light.During an irradiation process, the highly charged ions would penetrateinto the material (sample) and lose their energy through differentroutes. All the irradiation experiments at UNILAC were performed at roomtemperature. Usually a fluence of 10⁴ to 5·10⁸ ions/cm² was applied fornanopore fabrication.

Sensitization

In case of PET, polymer substrates were exposed to UV light (320 nm) for60 minutes on each side, leading to photo-oxidative degradation.

Ion Track-Etching

The fabrication of cylindrical nanopores in polymer substrates wasconducted through symmetric chemical etching of latent ion tracks usingalkali hydroxide solution. The track etching was carried out in a doublewalled isothermal bath, which is half-filled with 2M sodium hydroxide(NaOH) solution. The temperature of etching solution was maintained at50° C. by circuits of heating and cooling water flowing through thedouble walls of the beaker. The ion tracked polymer substrates werefirst fixed in the sample holders as shown in FIG. 2A. Then this sampleholder with substrates was immersed in the preheated etching bath (FIG.2B). FIG. 2C shows a simplified scheme for the fabrication ofcylindrical nanopores in the etching bath. Under these conditions thepore diameter scaled linearly with etching time at a rate of ˜5.4 nm perminute. After the etching, the sample holders along with polymersubstrates were taken out from the etching bath and rinsed several timeswith deionized water. In this setup the etchant can attack and dissolvethe latent ion tracks in polymer membrane from both sides. Therefore,this etching process is considered as symmetrical etching.

Generation of Functional Groups

The heavy ion irradiation and subsequent chemical etching processemployed for production of track-etched nanopores resulted in thecleavage of chemical bonds in the polymeric material. As a result,chemical groups were generated on the membrane surface and the channel.

Example 2 LPE Growth of HKUST-1 on Nanoporous Polymer

HKUST-1 continuous thin film layer was grown on carboxylatefunctionalized nanoporous polymer (NPP) using liquid phase epitaxy (LPE)approach. A solution of 1 mM copper acetate, Cu(COOCH₃)₂.H₂O, LobaChemie, 98%, was prepared by dissolving 19.9 mg of Cu(COOCH₃)₂.H₂O in100 mL ethanol, and 1 mM linker solution was prepared by dissolving 21.1mg of the 1,3,5-benezene tricarboxylic acid (BTC, Acros Organics, 98%)in 100 mL ethanol. In a typical procedure, NPP was activated by washingwith de-ionized water and ethanol 3 times at RT (22° C.). The activatedNPP was attached to the tip of the glass slide using plastic tape. Thesubstrate was then mounted in the sample holder of the robot (SilarCoating System, model HO-TH-03). The robot was programmed to carry outrepeating cycles of HKUST-1 growth at room temperature on the NPPaccording to the following sequence (see FIG. 4): immersion of the NPPin the metal solution for 5 min followed by drying in air for 3 min,this followed by 2 times consecutive washings in fresh ethanol for 3min. The resulting NPP with the metal attached (NPP-M) was immersed inthe linker solution for 10 min followed by drying for 3 min and theresulting NPP-M with the linker attached (NPP-ML) was washed again withfresh ethanol for 2 times (3 min each) and dried in air for 3 min. Thisprocess was repeated according to the assigned cycle number.

PET polymer having 12 micron long and 300 nm wide ionic nanoporechannels with —COOH groups were used to grow a robust, well-intergrownHKUST-1 coated flexible membrane via the LPE approach. Thecharacteristic membrane is the first MOF flexible membrane having ionicnanopores with no defects.

Example 3 Characterization of LPE Growth of HKUST-1 on NanoporousPolymer

The morphology of the ionic nanoporous polymer and Cu₃(BTC)₂ coatedmembrane was evaluated by optical microscopy and a field-emissionscanning electron microscope (FESEM: JEOS JSM 6700F). X-ray diffraction(XRD) patterns of the MOF membrane was obtained on a Siemens D5005diffractometer with Cu-Kα radiation (λ=1.5418 Å). A soap-film flow meterwas used to measure the flux of the gas, and the gas that penetrated themembrane was analyzed by gas chromatograph (HP6890).

As shown in FIGS. 6A-6F, it was found that lower concentrations (0.5 and1.0 mmol) of metal ion and organic linker favor continuous HKUST-1growth. Increases in concentration produced bigger particles anddecreased growth continuity. At a maximum concentration tested of 2.5mmol, a distortion in the crystal structure was observed.

As shown in FIGS. 7A-7F, small crystal growth of the HKUST-1 layer wasobserved in shorter time periods of 2 and 4 min in metal and linkersolutions, respectively. The sample prepared with 5 and 10 min was notmuch different in crystal growth except a small increase in crystalsize. The sample prepared with 10 and 20 min showed good uniform growth,however many large particles were seen along with small crystalparticles. Crystal growth and agglomeration of particle starts startedto appear in samples prepared with even longer time.

According to FIGS. 8A-8D, the HKUST-1 MOFs particles can be seen insidethe pores and the pores were filled by MOFs.

As shown in FIGS. 9A-9F, the HKUST-1 particles covered the pores andsurface of the substrate in a successive fashion. The number ofpreferred oriented HKUST-1 crystals increased as the number of cyclesincreased. This reveals the orientation of —COOH groups in the pores andon the surface of the polymer substrate.

As shown in FIGS. 10A-10F, the surface growth the particles of HKUSTcould be seen consistent with the growth in the nanopore channels ofsubstrate. After 60 cycles the pores started to get filled, while after80 and 100 cycles the pores were even more obviously filled. Thedistortion and opening of the pores was caused by sample preparation(e.g. tearing) and by the high voltage (20 kv) of the FESEM beam.

According to FIG. 11A, the HKUST-1 particles were shown in highmagnification. The crystal structure and EDX results in FIG. 11Bconfirmed the growth of HKUST-1 in NPP.

According to FIGS. 12A and 12B, the successive growth of HKUST-1 on NPPwas demonstrated by their experimental XRD patterns in comparison to thebare NNP.

As shown in FIGS. 13A and 13B, it was revealed that pure NPP showed noabsorption compared to the HKUST-1/NPP. As the growth thicknessincreased, the absorption band increased.

As shown in FIGS. 15A-15H, the strong adhesion of the MOF layer to theNPP was tested after preparation of the flexible MOF membrane. In thisanalysis four pieces of HKUST-NPP membrane (after 100 cycles growth)were soaked for 1 h in toluene and then sonicated for 5, 10, 60, and 300seconds. The membranes then separated, washed with ethanol three timesand examined by SEM. The physical appearance and FESEM analysis revealedthat the MOF material was strongly bonded to the NPP substrate. Such astrong bonding between the small particles of HKUST to the polymersubstrate might be the reason for absence of defects during rolling,which suggests a highly anchored, continuous and flexible MOF membrane.

As shown in FIGS. 16A-16C, the PET NPP polymer showed thermal stabilityat up to 400° C. HKUST-1/NPP membrane started to show weight loss at100° C. which was due to the adsorbed moisture and ethanol during layerby layer (LBL) process. At 300° C. the degree of weight loss was highwhich reflected the thermal stability of MOF/NPP. The residue of theparent NPP was zero, while the residue of the HKUST-NPP was around 5%which reflected the formation of CuO as a result of oxidation of HKUST-1in air.

As shown in FIGS. 17A-17B, the color of the membranes changed from greento blue which is consistent with literature reported properties ofHKUST-1 under temperature change.

As shown in FIG. 19, the BET isotherm was measured at liquid nitrogentemperature (77 K). Filled and open symbols represent adsorption anddesorption branches, respectively. The connecting curves are guides forthe eye. The resulting isotherm of type II with a BET surface area of220 m².g⁻¹ revealed the porosity of HKUST-1 in NPP.

Example 4 Nano Indentation of Membranes

In order to ensure the physical stability and flexibility, theinvestigation of nano-mechanical properties of membranes werecharacterized by nano-indentation technique.

Example 5 Gas Separation Analysis

For the assessment of different membranes effectiveness for gasseparation applications, dense and spongy membranes were subjected togas permeation experiments using constant volume/variable pressure CV/VPapparatus (FIG. 23). Each membrane was separately loaded into themembrane cell by fixing the membrane on a stainless-steel mesh from thepermeate side and by a rubber O-ring from the feed side. The membraneholder was assembled in the CV/VP apparatus and subjected to vacuum fromboth sides for 24 hrs at 35° C. to ensure the complete removal ofresidual solvent molecules from the membrane. The sample was consideredcompletely activated, when a baseline pressure (25-35 mTorr) wasobtained and no further loss in pressure was noticed. And when the leakrate and the built-in pressure became ≤1×10⁻⁷ mTorr, the sample becameready for the permeation measurements. After the confirmation of theaccepted leak rate, single gas permeation measurement was carried out bypressurizing the membrane from the feed side with different gases,separately, adjusted at 2 bar (p_(up)). The change of the pressure inthe permeate side (dp_(down)) was monitored versus time (dt) and graphedfor each gas. Permeation curves for different gases and membranes arepresented in FIGS. 25-26. The time-lag (θ) was calculated from the graphand the steady state permeation rate (dp^(SS)/dt) was quested after 7-10times θ that is used in the calculation of the gas permeability(Equation 1).

$\begin{matrix}{P = {10^{10}( {\frac{{dp}_{d}^{SS}}{dt}\mspace{14mu} - \frac{{dp}_{d}^{LR}}{dt}} )\frac{V_{d}l}{( {p_{up} - p_{d}} ){ART}}}} & ( {{Equation}\mspace{14mu} 1} )\end{matrix}$

Single gas permeability was measured for H₂, O₂, N₂, CO₂ and CH₄. Idealselectivities (α^(i) _(j)) of the more permeable gas (i) versus gas (j)were calculated from the obtained single gas data. Defect-free membranequality was confirmed from the obtained time-lag and the resulting O₂/N₂selectivity, which is higher than Knudsen diffusion selectivity (1.1)².

TABLE 1 Comparison of the single gas permeance and selectivities valuesmeasured on pure HKUST-1 membranes found in literature Separation factorSynthesis Perm H₂/ H₂/ H₂/ H₂/ H₂/ H₂/ H₂/ H₂/ MOF Support Method TempH₂ O₂ N₂ CO₂ CH₄ C₂H₄ C₂H₆ C₃H₈ C₃H₆ Year Ref HKUST-1 Copper net 4.604.52 7.8 2009 [11] HKUST-1 Alumina Seed 7.5 5.1 5.7 2010  [8] HKUST-1Alumina Hydro- 3.7 3.5 2.4 2011  [9] thermal HKUST-1 Hollow Secondary8.66 13.56 6.19 2012 [12] ceramic growth fibers 8.91 9.24 11.20 2012[32] (HCFs) HKUST-1 Anodic Seed 1.8 4.4 4.2 4.8 3.0 2013 [13] aluminum1.8E⁻⁷ oxide (AAO) HKUST-1 Copper 1.58 3.3 3.4 4.2 2.5 2013 [14]hydroxide nanostrand CHN HKUST-1 PVDF 2.01 6.5 8.1 3.4 2014 [15] HKUST-1Stainless EPD 3.9 4.6 2015 [16] steel HKUST-1 CuO 1.76 3.6 4.2 2.9 2016[17] (6.7) (5.6) (7.7) HKUST-1 IL_CS 2017 [18] HKUST-1 Alumina, 4.5-2013 [10] Au 8.4 HKUST-1 Nano- LPE 22 4.2 11.1 1.2 10.6 5.21 12.28 66.9113.6 2018 This porous work polymer (NPP) Refs [11]: Guo H, Zhu G,Hewitt I J, Qiu S. (2009) Journal of the American Chemical Society 131:1646-1647; [8]: Guerrero V V, Yoo Y, McCarthy M C, Jeong H-K. (2010)Journal of Materials Chemistry 20: 3938-3943; [9]: Nan J, Dong X, WangW, Jin W, Xu N. (2011) Langmuir 27: 4309-4312; [12]: Zhou S, Zou X, SunF, Zhang F, Fan S, Zhao H, Schiestel T, Zhu G. (2012) Journal ofMaterials Chemistry 22: 10322-10328; [32]: Ben T, Lu C, Pei C, Xu S, QiuS. (2012) Chemistry-A European Journal 18: 10250-10253; [13]: Mao Y, CaoW, Li J, Sun L, Peng X. (2013) Chemistry-A European Journal 19:11883-11886; [14]: Mao Y, shi L, Huang H, Cao W, Li J, Sun L, Jin X,Peng X. (2013) Chemical Communications 49: 5666-5668; [15]: Mao Y, Li J,Cao W, Ying Y, Sun L, Peng X. (2014) ACS Applied Materials & Interfaces6: 4473-4479; [16]: Zhu H, Liu H, Zhitomirsky I, Zhu S. (2015) MaterialsLetters 142: 19-22; [17]: Guo Y, Mao Y, Hu P. Ying Y, Peng X. (2016)ChemistrySelect 1: 108-113; [18]: Fernández-Barquín A, Casado-CoterilloC, Etxeberria-Benavides M, Zuñiga J, Irabien A. (2017) ChemicalEngineering & Technology 40: 997-1007; and [10]: Hurrle S, Friebe S,Wohlgemuth J, Wöll C, Caro J, Heinke L. (2017) Chemistry-A EuropeanJournal 23: 2294-2298, each incorporated herein by reference in theirentirety.

TABLE 2 Comparison of the CO₂ gas separation from hydrocarbons found inliterature Separation factor Synthesis Perm CO₂/ CO₂/ CO₂/ CO₂/ MOFSupport Method Temp CO₂ Ethane Ethylene Propane Propylene Year Ref ZIF-8CPI Mixed matrix 779 10.48 2013 [33] Pristine Alumina Thin Film 111 2.534] PU membrane XPU- 76.9 3.9 [34] HDA XPU- 57.9 4.4 [34] ODA HKUST-1NPP LPE 22 4190 6.16 14.51 79.05 134.25 2018 This work Refs [33]: AskariM, Chung T-S. (2013) Journal of Membrane Science 444: 173-183; and [34]:Isfahani A P, Ghalei B, Wakimoto K, Bagheri R, Sivaniah E, Sadeghi M.(2016) Journal of Materials Chemistry A 4: 17431-17439, eachincorporated herein by reference in their entirety.

TABLE 3 Comparison of the CO₂ gas separation from nitrogen and naturalgas CO₂/ CO₂/ MOF Polymer Wt % P(CO₂) CH₄ N₂ Year Ref IRMOF-1 Ultem 102.8 27.8 2009 [35] 20 3 26.3 2009 [35] HKUST-1 pdms 10 3000 34 8.9 2006[36] 40 2900 3.6 8.9 2006 [36] psf 5 6.5 18 20 2006 [36] 10 7.5 21.5 252006 [36] ZIF-8 PPEEs 10 5.4 22.9 30.1 2011 [37] 30 50 20.8 24.5 2011[37] MIL- PMDA- 5 0.3 72.1 34.8 2012 [38] 53(AI) ODA ZIF -8 PIM-1 102012 [39] 29 2012 [39] ZIF-8 PBI/PI 10 2012 [39] ZIF-8 10 2012 [39]ZIF-8 10 2012 [39] ZIF-8 PBI 30 2013 [40] ZIF-8 PIM4 11 4815 15 19.32013 [41] 28 4270 18.6 21.9 2013 [41] 36 6820 13.4 17.9 2013 [41] 436300 14.7 18.0 2013 [41] ZIF-90 PBI 10 2013 [42] HKUST-1 PPO 10 68.716.4 16 2013 [43] ZIF-8 6FDA- 33.3 486.5 15.6 13.4 2013 [44] dureneMIL-68 psf 4 4.7 12 2013 [45] ZIF-8 PBI-BuI 10 2.3 57 26.8 2014 [46] 305.2 43.6 16 2014 [46] DMPBI- 10 3.8 47.2 21.7 2014 [46] BuI 30 53.9 15.711.3 2014 [46] DBzPBI- 10 25.8 15.9 12.9 2014 [46] BuI 20 89.8 11.6 14.32014 [46] c-MOF-5 PEI 25 5.4 23.4 28.4 2014 [47] ZIF-71 6FDA- 10 180516.1 14.9 2014 [48] durene 20 4006 12.8 12.9 2014 [48] 30 7750 9.53 11.52014 [48] ZIF-8 PI/PSF 30 19 42 2017 [49] UiO-66 PIM-1 30 4500 22 282017 [50] ZIF-11 6FDA- 10 109 31 2017 [51] DAM 30 73 30 2017 UiO-66graphite 2017 [52] oxide ZIF-90 6FDA-TP 10 26 42 24 2017 50 63 36 202017 NH₂-MIL- VTEC 1 2017 53 FeBTC PEBAX 5 80 19.3 2018 [53] 30 402 182018 NH₂-MIL- Cellulose 15 52 28 2018 [54] 53(Al) Acetate ZIF-94 6FDA-10 780 24.7 2018 [55] DAM 20 960 23.6 2018 30 1000 17.8 2018 40 200022.9 2018 UiO-66 6FDA- 17 57 48 2018 [56] Bisp 6FDA- 17 43 57 2018 ODA6FDA- 8 1728 32 2018 DAM HKUST-1 NPP 100 4190 13.16 12.51 This work Refs[35]: Liu C, McCulloch B, Wilson S T, Benin A I, Schott M E. (2009).Metal organic framework-polymer mixed matrix membranes, U.S. Pat. No.7,637,983; [36]: Car A, Stropnik C, Peinemann K-V. (2006) Desalination200: 424-426; [37]: Díaz K, López-González M, del Castillo L F, RiandeE. (2011) Journal of Membrane Science 383: 206-213; [38]: Ren H, Jin J,Hu J, Liu H. (2012) Industrial & Engineering Chemistry Research 51:10156-10164; [39]: Yang T, Shi G M, Chung T-S. (2012) Advanced EnergyMaterials 2: 1358-1367; [40]: Yang T, Chung T-S. (2013) InternationalJournal of Hydrogen Energy 38: 229-239; [41]: Bushell A F, Attfield M P,Mason C R, Budd P M, Yampolskii Y, Starannikova L. Rebrov A. BazzarelliF, Bernardo P, Carolus Jansen J. Lan{hacek over (c)} M, Friess K,Shantarovich V, Gustov V, Isaeva V. (2013) Journal of Membrane Science427: 48-62; [42]: Yang T, Chung T-S. (2013) Journal of MaterialsChemistry A 1: 6081-6090; [43]: Ge L, Zhou W, Rudolph V, Zhu Z. (2013)Journal of Materials Chemistry A 1: 6350-6358; [44]: Wijenayake S N,Panapitiya N P, Versteeg S H, Nguyen C N, Goel S, Balkus K J, MusselmanI H, Ferraris J P. (2013) Industrial & Engineering Chemistry Research52: 6991-7001; [45]: Seoane B, Sebastian V, Tellez C, Coronas J. (2013)CrystEngComm 15: 9483-9490; [46]: Bhaskar A, Banerjee R, Kharul U.(2014) Journal of Materials Chemistry A 2: 12962-12967; [47]: ArjmandiM, Pakizeh M. (2014) Journal of Industrial and Engineering Chemistry 20:3857-3868; [48]: Japip S, Wang H, Xiao Y, Shung Chung T. (2014) Journalof Membrane Science 467: 162-174; [49]: Shahid S, Nijmeijer K. (2017)Separation and Purification Technology 189: 90-100; [50]: Khdhayyer M R,Esposito E, Fuoco A, Monteleone M, Giorno L, Jansen J C, Attfield M P,Budd P M. (2017) Separation and Purification Technology 173: 304-313;[51]: Safak Boroglu M, Yumru A B. (2017) Separation and PurificationTechnology 173: 269-279; [52]: Castarlenas S, Téllez C, Coronas J.(2017) Journal of Membrane Science 526: 205-211; [53]: Dorosti F,Alizadehdakhel A. (2018) Chemical Engineering Research and Design; [54]:Mubashir M, Yeong Y F, Lau K K, Chew T L, Norwahyu J. (2018) Separationand Purification Technology 199: 140-151; [55]: Etxeberria-Benavides M,David O, Johnson T, Łozińska M M, Orsi A, Wright P A, Mastel S,Hillenbrand R, Kapteijn F, Gascon J. (2018) Journal of Membrane Science550: 198-207; [56]: Zamidi Ahmad M, Navarro M, Lhotka M, Zornoza B,Téllez C, Fila V, Coronas J. (2018) Separation and PurificationTechnology 192: 465-474; and [57]: Robeson L M. (2008) Journal ofMembrane Science 320: 390-400, each incorporated herein by reference intheir entirety.

1: A membrane, comprising: a polymer substrate having pore channels; anda metal-organic framework comprising a metal ion and an organic ligandcoordinated to the metal ion; wherein: the pore channels have an averagediameter of 0.1-2 μm and an average length of 2-100 μm; themetal-organic framework is disposed on a wall surface of the porechannels and an outer surface of the polymer substrate; and themetal-organic framework is present at an amount of 0.1-50 wt % relativeto a total weight of the membrane. 2: The membrane of claim 1, whereinthe metal-organic framework has an average thickness of 100-2,000 nm. 3:The membrane of claim 1, wherein the metal ion is an ion of at least onemetal selected from the group consisting of a transition metal, apost-transition metal, and an alkaline earth metal. 4: The membrane ofclaim 1, wherein the polymer substrate comprises at least one polyesterselected from the group consisting of poly(ethylene terephthalate),poly(trimethylene terephthalate), poly(butylene terephthalate),poly(ethylene naphthalate), and poly(cyclohexylenedimethyleneterephthalate). 5: The membrane of claim 1, wherein the wall surface ofthe pore channels and the outer surface of the polymer substrate aremodified with carboxylate groups. 6: The membrane of claim 4, whereinthe polymer substrate comprises poly(ethylene terephthalate). 7: Themembrane of claim 1, wherein the organic ligand has at least twocarboxylate groups. 8: The membrane of claim 7, wherein the organicligand is benzene-1,3,5-tricarboxylate. 9: The membrane of claim 3,wherein the metal ion is an ion of at least one metal selected from thegroup consisting of Cu, Zn, Fe, Ni, Co, Mn, Cr, Cd, Mg, Ca, and Zr. 10:The membrane of claim 1, wherein the metal-organic framework comprisesHKUST-1. 11: The membrane of claim 1, which has an ultraviolet visibleabsorption with an absorption peak of 500-800 nm. 12: The membrane ofclaim 1, which has a BET surface area of 100-500 m²/g. 13: A method ofproducing the membrane of claim 5, the method comprising:ion-irradiating a polymer substrate with heavy ions to form a polymersubstrate having latent tracks; exposing the polymer substrate havinglatent tracks to a light to form a sensitized polymer substrate; etchingthe sensitized polymer substrate with an etchant to form a polymersubstrate having pore channels; immersing the polymer substrate havingpore channels in a first solution comprising the metal ion to form ametal ion coated polymer substrate; immersing the metal ion coatedpolymer substrate in a second solution comprising the organic ligand toform a metal-organic framework coated polymer substrate; and alternatingimmersions in the first solution and the second solution for up to 200cycles, thereby forming the membrane; wherein: the pore channels have anaverage diameter of 0.1-2 μm and an average length of 2-100 μm; and thewall surface of the pore channels and the outer surface of the polymersubstrate having pore channels are modified with carboxylate groups. 14:The method of claim 13, wherein the heavy ions have a fluence of10³-10¹⁰ heavy ions per square centimeter and an average kinetic energyof 5-25 MeV per nucleon. 15: The method of claim 13, wherein the metalion is present in the first solution at a concentration of 0.01-100 mMand the organic ligand is present in the second solution at aconcentration of 0.01-100 mM. 16: The method of claim 13, whereinimmersing the polymer substrate having pore channels in the firstsolution comprising the metal ion is performed at a temperature of 4-60°C. for 1-60 min per cycle. 17: The method of claim 13, wherein immersingthe metal ion coated polymer substrate in the second solution comprisingthe organic ligand is performed at a temperature of 4-60° C. for 1-60min per cycle. 18: The method of claim 13, wherein the etchant is asolution comprising sodium hydroxide at a concentration of 0.5-5 M. 19:A method of recovering a first gas from a gas mixture comprising thefirst gas and a second gas, the method comprising: delivering the gasmixture into a feed side of a chamber comprising the membrane of claim 1that divides the chamber into the feed side and a permeate side, suchthat at least a portion of the first gas permeates the membrane; andrecovering from the permeate side a stream enriched in the first gascompared to the gas mixture. 20: The method of claim 19, wherein thefirst gas is hydrogen, carbon dioxide, or both, and the second gas is atleast one selected from the group consisting of oxygen, nitrogen,methane, ethylene, ethane, propylene, and propane.